A. Field of the Invention
This invention relates generally to particulate material transferring systems, and more particularly to a system for injecting gravel into a fluid carrying flow line for use in gravel or sand packing operations.
B. Description of the Prior Art
A common problem encountered in oil and gas production is the control of particles from unconsolidated and disintegrating formations so that they may not enter the well. Such control diminishes the destructive influence of the sand scouring on well equipment and tends to reduce maintenance cost. Also, such control makes equipment repair and well clean out operations less frequent, thereby enabling the well to produce for a greater period of time than would otherwise be the case.
One method for controlling such unconsolidated and disintegrating material is known as gravel or sand packing which involves surrounding the tubing through the producing formation with a filter bed of gravel or coarse sand. In industry usage, gravel has particle sizes in the range of 4 to 10 or 14 mesh and sand has particles ranging in size from 20 to 40 mesh. However, for purposes hereof and as used herein, the packing medium shall be referred to as gravel, which shall include both gravel and sand.
One common method for gravel packing is by circulation, in which a slurry is forced of gravel and a fluid, such as oil or light weight drilling fluid. The slurry is circulated into the production zone either normally or reversed where the gravel is deposited. The circulating fluid is returned to the surface either through the annulus, or through the tubing in case of reverse circulation. An example of a method of sand packing is disclosed in U.S. Pat. No. 2,952,318.
A problem in gravel packing is in the preparation of the gravel and fluid slurry. Typically, the gravel is poured into the fluid in a tank and then the contents of the tank are sucked through the inlet of a pump and discharged into the well. Such a method leads to an inconsistent slurry which at times has too high a concentration of gravel and at other times too low. Additionally, the relatively large abrasive gravel particles cause wear in the pump, which leads to premature pump failures.
Accordingly, it is an object of the present invention to overcome the shortcomings of the prior art. More specifically, it is an object of the present invention to provide an apparatus and system for forming a uniform gravel and fluid slurry. It is a further object of the present invention to provide an apparatus and system which is capable of producing a gravel and fluid slurry wherein the relative proportions of gravel and fluid may be controlled and varied, thereby to optimize gravel packing. It is a further object of the present to provide an apparatus and system which is adapted to inject a gravel and fluid slurry into a well without running the slurry through a pump.